Thin polished plates such as silicon wafers and the like are a very important part of modern technology. A wafer, for instance, may refer to a thin slice of semiconductor material used in the fabrication of integrated circuits and other devices. Other examples of thin polished plates may include magnetic disc substrates, gauge blocks and the like. While the technique described here refers mainly to wafers, it is to be understood that the technique also is applicable to other types of polished plates as well. The term wafer and the term thin polished plate may be used interchangeably in the present disclosure.
Semiconductor manufacturing processes are typically run in batches called lots. A lot, or a wafer lot, is defined as a number of wafers processed together as a single group. In certain instances, different priorities may be assigned to different lots to indicate how quickly those lots need to be processed. For instance, lots that need to be shipped sooner may be assigned a higher priority than others.
One approach to increase manufacturing throughput of high priority lots is to limit defect inspections to only critical layers and bypass defect inspections of non-critical layers. More specifically, certain process steps of the semiconductor manufacturing process may be identified as critical steps while the rest of the process steps may be considered non-critical. Defect inspections may be performed after the critical steps, but bypassed after the non-critical process steps to help reduce the overall time consumption. It is noted, however, that since this approach is entirely based on predetermined decisions, it is very likely for the defect inspections to miss potential process issues. It is also noted that the likelihood of missing yield excursion may increase as the number of process steps that are predetermined to be critical decreases.